Question : A boat can travel at a speed of 15 km/hr in still water. If the speed of the stream is 5 km/hr, find the time taken by the boat to go 80 km downstream.
Option 1: 3 hr
Option 2: 4 hr
Option 3: 6 hr
Option 4: 5 hr
Correct Answer: 4 hr
Solution :
Given,
Speed of boat in still water = 15 km
Speed of stream = 5 km/hr
Speed of Downstream = Speed of boat + Speed of stream = 15 + 5 = 20 km/hr
We know, Time = $\frac{\text{Distance}}{\text{Speed}}$
$\therefore$ Time taken = $\frac{80}{20}$ = 4 hr
Hence, the correct answer is 4 hr.
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